Xamarin.Forms change UI language at runtime (XAML)

When i encountered that challenge in a project I resolved it by using a simple class ResourceLoader and making use of INotifyPropertyChanged.

You can access the Instanceproperty from anywhere and change the culture. All String that are bound to the index would update.

The ResourceManager instance injected into the constructor must be set up appropriately.

public class ResourceLoader : INotifyPropertyChanged
{
    private readonly ResourceManager manager;
    private CultureInfo cultureInfo;

    public ResourceLoader(ResourceManager resourceManager)
    {
        this.manager = resourceManager;
        Instance = this;
        this.cultureInfo = CultureInfo.CurrentUICulture;
    }

    public static ResourceLoader Instance { get; private set; }

    public string GetString(string resourceName)
    {
        string stringRes = this.manager.GetString(resourceName, this.cultureInfo);
        return stringRes;
    }

    public string this[string key] => this.GetString(key);

    public void SetCultureInfo(CultureInfo cultureInfo)
    {
        this.cultureInfo = cultureInfo;
        this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(null));
    }

    public event PropertyChangedEventHandler PropertyChanged;
}

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To display the localized strings in your application you need to bind through the indexer like so:

<Label Text="{Binding [Test], Source={x:Static ResourceLoader.Instance}}" />

Since it is now bound it should update when you call ResourceLoader.SetCultureInfo because the Item[] ‘PropertyName’ is causing bound controls to re-fetch the values to their bound keys.

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Update

I just tested it if i was talking bogus and for some reason the property changed didn’t work. I’ve added a different approach below, which is close to what i’m using in production i urge you to add some kind of weak reference ‘caching’ instead of the simple list holding all the string resources (otherwise they will be kept forever)

I’m keeping above for reference.

public class ResourceLoader
{

    public ResourceLoader(ResourceManager resourceManager)
    {
        this.manager = resourceManager;
        Instance = this;
        this.cultureInfo = CultureInfo.CurrentUICulture;
    }

    private readonly ResourceManager manager;
    private CultureInfo cultureInfo;

    private readonly List<StringResource> resources = new List<StringResource>();

    public static ResourceLoader Instance { get; private set; }

    public StringResource this[string key] {
        get { return this.GetString(key); }
    }

    public StringResource GetString(string resourceName)
    {
        string stringRes = this.manager.GetString(resourceName, this.cultureInfo);
        var stringResource = new StringResource(resourceName, stringRes);
        this.resources.Add(stringResource);
        return stringResource;
    }

    public void SetCultureInfo(CultureInfo cultureInfo)
    {
        this.cultureInfo = cultureInfo;
        foreach (StringResource stringResource in this.resources) {
            stringResource.Value = this.manager.GetString(stringResource.Key, cultureInfo);
        }
    }

}

StringResource:

public class StringResource : INotifyPropertyChanged
{

    public StringResource(string key, string value)
    {
        this.Key = key;
        this.Value = value;
    }

    private string value;

    public string Key { get; }

    public string Value {
        get { return this.value; }
        set {
            this.value = value;
            this.OnPropertyChanged();
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

}

XAML Binding

<Label  Text="{Binding [ResourceKey].Value, Mode=OneWay, Source={x:Static local:ResourceLoader.Instance}}" 
           />

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Update 2

Came across this link where they implemented it similarly to my first approach. Maybe you can give it a try.

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Update 3

Fixed the first approach. Both are working now. What was needed was this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(null)); instead of this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(Item[]));